This application claims priority to German patent application number 101 41 243.6 filed Aug. 23, 2001.
This invention relates to an inner shell for a roof module in sandwich construction, comprising an inner layer and a holding layer in which a reinforcement layer is embedded, the reinforcement layer being arranged within the holding layer at a side thereof which faces the inner layer.
Such an inner shell is provided for being connected with an outer shell in order to form a roof module in sandwich construction. In this arrangement, the holding layer, with its side facing away from the inner layer, is connected with the outer shell by means of gluing, clipping on or by other measures. As the reinforcement layer is arranged within the holding layer at the side thereof which faces the inner layer, there will be a maximum distance between the neutral line, in case of bending loads, of the roof module and the reinforcement layer; thus, the reinforcement layer offers the highest possible contribution to the strength of the roof module.
Hitherto, a so-called spacer has been incorporated in the foam of the holding layer, which spacer has ensured that the reinforcement layer is located during foaming on the side of the holding layer facing the inner layer. A coarsely porous spacer mat could be used as spacer. The spacer mat, however, is a costly component.
The object of the invention therefore consists in providing an inner shell of the type initially mentioned, which with small piece cost comprises a reinforcement mat that is precisely positioned in the holding layer. It is further the object of the invention to provide a method of producing such inner shell.
According to the invention, an inner shell for a roof module in sandwich construction comprises an inner layer and a holding layer in which a reinforcement layer is embedded. The reinforcement layer is arranged within the holding layer at a side thereof which faces the inner layer. The holding layer is provided with pocket-like recesses on its side facing away from the inner layer which extend as far as to the reinforcement layer. The pocket-like recesses are the consequence of the method employed for producing the inner shell. With this method, a foaming mold is made available which on one side is provided with nub-like projections. An inner layer is laid into the open foaming mold and a reinforcement layer is placed on the inner layer. An expandable material is then applied onto the reinforcement layer, such material being capable of forming a holding layer in the cured state. Next, the foaming mold is closed so that the projections rest at the reinforcement layer and hold it against the inner layer, and the expandable material is cured so that the reinforcement layer adjoining the inner layer is embedded into the holding layer during foaming. Positioning the reinforcement layer in the holding layer is thus not obtained any longer by a component which is embedded into each inner shell during foaming, but through the design of the foaming mold that is used for the foaming operation. In adaptation to the respective demands, the size of the recesses produced in the holding layer and of the protrusions provided in the foaming mold, respectively, can be used as a trade-off between numerous parameters which are contrary in part. The lower limit for the portion of protrusions of the entire surface area is predefined by the flexibility of the reinforcement layer; i.e., the recesses have to be arranged so close to each other that the reinforcement layer can not go away from the inner layer also in the intermediate regions where it is not pressedxe2x80x94in the foaming moldxe2x80x94against the inner layer by the protrusions. The upper limit for the portion of recesses of the entire surface area is predefined by the required minimum strength of the holding layer as well as by the surface area, made available by it, for being glued together with the outer shell; the webs remaining between the recesses must have specific minimum cross-sections and a specific minimum surface area. The size of the recesses has still further effects. The recesses form hollow chambers in the roof module which are of advantage in terms of acoustic properties. These effects can be optimized by the design of the recesses. In addition, the volume of the holding layer is reduced due to these recesses, so that a smaller amount of expandable material has to be introduced during production. Costs are further reduced thereby. As long as the inner and outer shells are not glued together, the recesses in the holding layer also reduce the strength of the inner shell, so that the latter can be folded more easily. Finally, the recesses reduce that surface area of the holding layer that is glued to the outer shell. Thereby, the separability of inner and outer shells is facilitated during recycling. Size and number of the recesses may differ from each other in distinct regions of the roof module, in order to make use of differing properties in these regions.
Advantageous designs of the invention will be apparent from the subclaims.